1. Field of the Invention
The present invention generally relates to an image display device and a laser light source device.
2. Description of the Related Art
Some image display devices incorporating video devices (spatial modulation elements) that do not emit light themselves, such as projection televisions and projectors, adopt a laser light source device that uses a semiconductor laser as a light source device. A laser light source device may be designed to include laser elements having different wavelengths such as red, green, and blue wavelengths.
The outputs of semiconductor lasers vary in accordance with the temperature of the laser element and ambient temperature. The outputs of the laser elements of different wavelengths have to be kept constant to stabilize the white balance and the brightness on the screen. Moreover, a laser light source device in general performs automatic power control (APC), in addition to temperature control for keeping the laser elements at a certain temperature, so that the optical output can be kept constant. The APC control here means adjustment of the amount of current that drives each laser element so as to stabilize the optical output of the semiconductor laser.
Typical APC control systems include a system of detecting a laser beam slightly emitted from the end surface opposite to the semiconductor laser beam emitting end surface, and a system of guiding part of the emission beam of the semiconductor laser into a different direction and detecting this beam (see, for example, Japanese Patent Application Laid-open No. 2004-342278). Because the detection accuracy is insufficient with the former system, the latter system is widely used.
To perform APC control in the above laser light source device that incorporates a semiconductor laser as a light source, the output value (the amount of light) has to be detected for each of the laser elements of the laser light source device. However, if, a light amount detecting circuit is arranged for each of the laser elements of different wavelengths, light amount detecting circuits, the number of each of which is the same as that of the types of wavelengths, and optical paths for the light amount detecting circuits are required. This is disadvantageous in cost and size.
Moreover, a structure may be designed to share an optical path and a light amount detecting circuit by adopting a sensor that has a wavelength resolution capacity, such as a color filter-provided sensor. However, most color filters that are commonly available at low cost cannot completely separate the amounts of beams emitted from different laser elements. With such a color filter, the output of a single laser element of a certain wavelength tends to be inaccurately detected as the outputs of plural laser elements of different wavelengths, and thus the APC control cannot be performed with high accuracy. In addition, a light amount detecting circuit incorporating a color filter that can accurately separate the amounts of beams emitted from different laser elements is impractical from the aspect of cost.